Multiphase interleaved forward power converters including clamping circuits

ABSTRACT

A multiphase interleaved forward power converter includes an inductor and first and second subconverter comprising respective transformers. The converter also includes first and second drives configured to respectively operate the first and second subconverters with cycling periods comprising a conduction period, a reset period, and an idle period. The first and second drives are also configured to phase shift the cycling periods in each subconverter such that the conduction period of the subconverter is at least partially complementary to the idle period of the other subconverter. The second drive also clamps a voltage across a winding of the transformer of the first subconverter to substantially prevent a first resonance voltage from propagating in the first subconverter during the idle period of the first subconverter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. applicationSer. No. 14/955,787 filed Dec. 1, 2015, the entire disclosure of whichis incorporated herein by reference.

FIELD

The present disclosure relates to multiphase interleaved forward powerconverters including clamping circuits.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Forward power converters are DC/DC converters that use a transformer tochange its output voltage and provide isolation. Frequently, multipleforward power converters are coupled together to form a multiphaseinterleaved forward power converter. In such cases, each power converteris phase shifted from each other so that one converter conducts at atime. For example, each power converter includes a cycling conductionperiod, reset period, and idle period. Typically, when one of theconverters is in its conduction period, the other converter(s) are intheir reset period or idle period.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

According to one aspect of the present disclosure, a multiphaseinterleaved forward power converter includes an inductor, a firstsubconverter comprising a first transformer coupled to an output of thefirst subconverter, and a first clamping circuit comprising a switchingdevice coupled to the at least one winding of the first subconverter.The multiphase interleaved forward power converter also includes asecond subconverter comprising a second transformer coupled to an outputof the second subconverter. The first and second transformers have atleast one winding. The multiphase interleaved forward power converteralso includes first and second drives configured to respectively operatethe first and second subconverters with cycling periods comprising aconduction period during which power is provided to the output of therespective first or second subconverter via the respective first orsecond transformer, a reset period during which energy stored in therespective first or second transformer is released to reset therespective first or second transformer, and an idle period between thereset period and the conduction period. The first drive is furtherconfigured to phase shift the cycling periods in the first subconvertersuch that the conduction period of the first subconverter is at leastpartially complementary to the idle period of the second subconverter.The second drive is further configured to phase shift the cyclingperiods in the second subconverter such that the conduction period ofthe second subconverter is at least partially complementary to the idleperiod of the first subconverter and clamp a voltage across a winding ofthe transformer of the first subconverter to substantially prevent afirst resonance voltage from propagating in the first subconverterduring the idle period of the first subconverter. The output of thefirst subconverter is coupled in parallel with the output of the secondsubconverter, and the outputs of the first and second subconverters arecoupled to the inductor.

According to another aspect of the present disclosure, a method forsubstantially preventing a resonance voltage from propagating in amultiphase interleaved forward power converter including an inductorcoupled to an output of a first subconverter including a firsttransformer and an output of a second subconverter including a secondtransformer, the outputs of the first and second subconverters coupledin parallel. The method comprises operating the first and secondsubconverters with respective cycling periods, each cycling periodcomprising a conduction period during which power is provided to therespective subconverter output via the respective transformer, a resetperiod during which energy stored in respective transformer is releasedto reset the respective transformer, and an idle period between thereset period and the conduction period. The method also includes phaseshifting the cycling periods in the first and second subconverters suchthat the conduction period of the first subconverter is at leastpartially complementary to the idle period of the second subconverterand such that the conduction period of the second subconverter is atleast partially complementary to the idle period of the firstsubconverter, and clamping a voltage across a winding of the transformerof the first subconverter to substantially prevent a first resonancevoltage from propagating in the first subconverter during the idleperiod of the first subconverter.

Further aspects and areas of applicability will become apparent from thedescription provided herein. It should be understood that variousaspects of this disclosure may be implemented individually or incombination with one or more other aspects. It should also be understoodthat the description and specific examples herein are intended forpurposes of illustration only and are not intended to limit the scope ofthe present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a block diagram of a multiphase interleaved forward powerconverter including clamping circuits each having a switching deviceaccording to one example embodiment of the present disclosure.

FIG. 2 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuits coupledto secondary transformer windings of the subconverters according toanother example embodiment.

FIG. 3 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuits coupledto primary side auxiliary transformer windings of the subconvertersaccording to yet another example embodiment.

FIG. 4 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuits coupledto secondary side auxiliary transformer windings of the subconvertersaccording to another example embodiment.

FIG. 5 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuitsincluding diodes coupled to secondary side auxiliary transformerwindings of the subconverters according to yet another exampleembodiment.

FIG. 6 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuitsincluding diodes coupled to primary side auxiliary transformer windingsof the subconverters according to yet another example embodiment.

FIG. 7 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter 6, but including threesubconverters and three clamping circuits according to another exampleembodiment.

FIG. 8 is a circuit diagram of a multiphase interleaved forward powerconverter including two subconverters and two clamping circuits eachcoupled to a secondary transformer winding of the subconverters andcontrolled based on a primary side switch control signal according toyet another example embodiment.

FIG. 9 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter 8, but including threesubconverters and three clamping circuits according to another exampleembodiment.

FIG. 10 is a circuit diagram of a multiphase interleaved forward powerconverter including three subconverters and three clamping circuits eachcoupled to a secondary transformer winding of the subconverters andcontrolled based on two primary side switch control signals according toyet another example embodiment.

FIG. 11 is a circuit diagram of a multiphase interleaved forward powerconverter including three subconverters and three clamping circuits eachcoupled to a secondary transformer winding of the subconverters andcontrolled based on a secondary side voltage signal according to anotherexample embodiment.

FIG. 12 is a circuit diagram of a multiphase interleaved forward powerconverter including three subconverters and three clamping circuits eachcoupled to a secondary transformer winding of the subconverters andcontrolled based on two secondary side voltage signals according to yetanother example embodiment.

FIG. 13 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter 10, but where theclamping circuits are coupled to secondary side auxiliary transformerwindings of the subconverters according to another example embodiment.

FIG. 14 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter 12, but where theclamping circuits are coupled to secondary side auxiliary transformerwindings of the subconverters according to another example embodiment.

FIG. 15 is a circuit diagram of a multiphase interleaved forward powerconverter including three subconverters and three clamping circuits eachincluding two switching devices coupled to secondary side auxiliarytransformer windings of the subconverters according to yet anotherexample embodiment.

FIG. 16 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter 15, but where theclamping circuits are controlled based on a secondary side voltagesignal according to another example embodiment.

FIG. 17 is a circuit diagram of a multiphase interleaved forward powerconverter including an inductor coupled to a reference output terminalof the converter according to yet another example embodiment.

FIG. 18 is a circuit diagram of a multiphase interleaved forward powerconverter including a rectification circuit having diodes with theiranodes coupled together according to another example embodiment.

FIG. 19 is a circuit diagram of a multiphase interleaved forward powerconverter including a rectification circuit having synchronousrectifiers according to yet another example embodiment.

FIG. 20 is a circuit diagram of a multiphase interleaved forward powerconverter including two clamping circuits and two subconverters having asingle switch forward converter topology according to another exampleembodiment.

FIG. 21 is a circuit diagram of a multiphase interleaved forward powerconverter similar to the forward power converter of FIG. 7, butincluding multiple switching circuits per subconverter according to yetanother example embodiment.

FIGS. 22A-22E are circuit diagrams of the subconverters of FIG. 21coupled to one or more power sources according to another exampleembodiment.

FIG. 23 is an exploded isometric view of a transformer employable in theforward power converter of FIG. 21, according to yet another exampleembodiment.

FIG. 24 is a top view of a transformer core for a three-phaseinterleaved forward converter according to another example embodiment.

FIGS. 25A and 25B illustrate waveforms of a drain to source voltage ofprimary side switches of a conventional two phase interleaved forwardpower converter and a two-phase interleaved forward power converterincluding two clamping circuits according to yet another exampleembodiment.

FIGS. 26A and 26B illustrate waveforms of a drain to source voltage ofprimary side switches of a conventional three phase interleaved forwardpower converter and a three phase interleaved forward power converterincluding three clamping circuits and experiencing a high idle timeresonant frequency according to another example embodiment.

FIGS. 27A and 27B illustrate waveforms of a drain to source voltage ofprimary side switches of a conventional three phase interleaved forwardpower converter and a three phase interleaved forward power converterincluding three clamping circuits and experiencing a low idle timeresonant frequency according to yet another example embodiment.

Corresponding reference numerals indicate corresponding parts orfeatures throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

According to one aspect of the present disclosure, methods are providedfor substantially preventing a resonance voltage from propagating in amultiphase interleaved forward power converter. The converter includesat least two subconverters phase shifted relative to each other suchthat a conduction period of one subconverter is at least partiallycomplementary to an idle period of another subconverter and vice versa.The method includes clamping a voltage across a winding of a transformerof one of the subconverters to substantially prevent a resonance voltagefrom propagating in that subconverter during its idle period.

Additionally, the method may further include clamping a voltage across awinding of a transformer of the other subconverter to substantiallyprevent a resonance voltage from propagating in that subconverter duringits idle period. Thus, resonance voltage may be substantially preventedin one or more subconverters of the multiphase interleaved forward powerconverter.

For example, during an idle time of one subconverter of a multiphaseinterleaved forward power converter, a voltage across a primary windingof its transformer is expected to equal substantially zero as thesubconverter is not conducting at this time. In some cases, however, thevoltage across the primary winding may resonant due to transformerleakage inductance, capacitance in primary side switch(es), etc. Thus,the voltage across the primary winding may swing from about zero voltsto about an input voltage of this forward power converter. Thisresonance voltage can create transformer conduction losses, increasedswitching losses in the primary side switch(es), etc.

Additionally, if the resonance voltage is terminated before a completeresonant cycle, additional DC bias voltage may be applied to thetransformer. This may increase flux density in the transformer causingadditional transformer core losses.

If, however, a current path is created to allow the transformer windingof the idle subconverter to conduct, a voltage across its idletransformer can be clamped and a DC bias voltage applied to thetransformer can be substantially prevented. As such, the voltage acrossthe transformer may be substantially prevented from resonating duringthe subconverter's idle period. Thus, a voltage across primary sidepower switches of the subconverters can remain relatively steady at adesired level. For example, if the subconverters include a two-switchforward converter topology (as further explained below), a voltageacross these switches can remain steady at about half the DC inputvoltage.

The current path may be created based one or more other subconverters inthe forward power converter. For example, the current path may becreated between a winding of the idle subconverter and a component ofone or more other subconverter(s) when the other subconverter(s) are ina conduction period. Thus, one or more conducting subconverters in theforward power converter may assist in clamping a voltage across thetransformer of an idle subconverter.

For example, and as further explained below, clamping in onesubconverter may be based on a parameter of the other subconverter(s) inthe forward power converter. This parameter may be, for example, acontrol signal for primary side switch(es) in the other subconverter(s),a sensed electrical parameter (e.g., a voltage, a current, etc.), etc.In some particular examples, the voltage may be a voltage of a secondarytransformer winding, a rectifier voltage, etc.

One or more of the methods disclosed herein may be implemented by aclamping circuit including, for example, any one of the clampingcircuits disclosed herein and/or another suitable clamping circuit. Asfurther explained below, FIGS. 1-20 illustrate various examplemultiphase interleaved forward power converters including clampingcircuits for creating current paths as explained herein.

For example, FIG. 1 illustrates a multiphase interleaved forward powerconverter according to one example embodiment of the present disclosureand is indicated generally by reference number 100. As shown in FIG. 1,the forward power converter 100 includes subconverters 102, 104 andclamping circuits 106, 108. The subconverters 102, 104 each include aninput 110, 112, an output 114, 116, and a transformer 118, 120 coupledbetween the input and the output. Each transformer 118, 120 includes atleast one winding 122, 124. As shown in FIG. 1, the output 114 of thesubconverter 102 is coupled in parallel with the output 116 of thesubconverter 104. The subconverters 102, 104 are phase shifted relativeto each other as explained above. The clamping circuits 106, 108 eachinclude a switching device 126, 128 coupled to the winding 122, 124.

The clamping circuits 106, 108 can clamp a voltage across the windings122, 124 to substantially prevent a resonance voltage from propagatingin the subconverter 102, 104 (e.g., in primary side switches, secondaryside switches, the transformer, etc.) during an idle period of thesubconverters. For example, the subconverter 102 may be in itsconduction period and the subconverter 104 may be in its idle period.The clamping circuit 108 may create a current path to allow the winding124 to conduct during the idle period of the subconverter 104 asexplained above.

The clamping circuit 106, 108 of FIG. 1 can be coupled across thewinding 122, 124 of the transformer 118, 120, respectively. For example,the switching device 126, 128 may be coupled across the winding 122,124.

The winding coupled to the clamping circuit may be a primary winding, asecondary winding, an auxiliary winding, etc. For example, FIG. 2illustrates a multiphase interleaved forward power converter 200including two subconverters 202, 204 each having a transformer T1, T2,and two clamping circuits 206, 208 each having a switching device 210,212 coupled across a secondary winding of the transformer T1, T2,respectively.

FIGS. 3 and 4 illustrate example multiphase interleaved forward powerconverters 300, 400 substantially similar to the power converter 200 ofFIG. 2, but including a clamping circuit having a switching devicecoupled across an auxiliary winding of a transformer. In particular, theforward power converter 300 includes clamping circuits 306, 308 eachhaving a switching device 310, 312 coupled across a primary sideauxiliary winding 302, 304, respectively, and the forward powerconverter 400 includes clamping circuits 406, 408 each having aswitching device 410, 412 coupled across a secondary side auxiliarywinding 402, 404, respectively.

FIG. 5 illustrates a multiphase interleaved forward power converter 500substantially similar to the power converter 400 of FIG. 4. The forwardpower converter 500 of FIG. 5 includes subconverters 502, 504 having thetransformers T1, T2 of FIG. 4, and clamping circuits 506, 508 coupled tothe subconverters 502, 504. The clamping circuits 506, 508 each includea diode 510, 512 coupled to the secondary side auxiliary winding 402,404, respectively. Thus, in the particular embodiment of FIG. 5, theswitching devices of the clamping circuits 506, 508 are diodes.Alternatively, one or both diodes 510, 512 can be replaced with anothersuitable switching device such as a switch (e.g., transistors, etc.) asfurther explained below.

As shown in FIG. 5, the auxiliary windings 402, 404, the diodes 510,512, and diodes Rect1, Rect2 of a rectification circuit (furtherexplained below) create a current path. Thus, in this example, theauxiliary windings 402, 404 and the diodes Rect1, Rect2 can beconsidered components of the clamping circuits 508, 506, respectively.

As explained above, the current paths allow the windings 402, 404 toconduct during a subconverter's idle period. For example, when thesubconverter 502 is in its conduction period and the subconverter 504 isin its idle period, a resonant voltage forces current to flow throughthe diode 512, the diode Rect1, and the auxiliary winding 404.Similarly, when the subconverter 504 is in its conduction period and thesubconverter 502 is in its idle period, a resonant voltage forcescurrent to flow through the diode 510, the diode Rect2, and theauxiliary winding 402.

Additionally, the diodes 510, 512 may prevent its respective clampingcircuit 506, 508 from conducting during a reset period of eachsubconverter 502, 504. For example, when the conduction period of thesubconverter 502 starts and the subconverter 504 is its reset period(before transitioning to its idle period), the diode 512 isreversed-biased. Thus, the clamping circuit 508 is prevented fromconducting due to the diode 512. As the subconverter 504 transitionsfrom its reset period to its idle period, a resonant voltage begins tobuild up. At some point, the diode 512 becomes forward-biased due to theincreasing resonant voltage, and therefore the clamping circuit 508 isallowed to conduct as explained above. As such, any attempt of the idlesubconverter resonance to prosper during the conduction period of theother subconverter can be substantially blocked by the appropriateclamping circuit.

FIG. 6 illustrates a multiphase interleaved forward power converter 600substantially similar to the power converter 500 of FIG. 5, but withclamping circuits coupled to primary side auxiliary windings. As shownin FIG. 6, the forward power converter 600 includes subconverters 602,604 and clamping circuits 606, 608. The subconverter 602 includes, aninput, the transformer T1 of FIG. 3 and primary side power switches 614,616 (collectively a switching circuit) coupled to the transformer T1.The subconverter 604 includes an input, the transformer T2 of FIG. 3,and primary side power switches 618, 620 (collectively a switchingcircuit) coupled to the transformer T2. The clamping circuits 606, 608include diodes 610, 612, respectively. The diodes 610, 612 functionsimilar to the diodes 510, 512 of FIG. 5, but are positioned on aprimary side of the transformers T1, T2.

The clamping circuit 606 creates a current path with the diode 610, theauxiliary winding 302 of the subconverter 602, and the power switch 620of the subconverter 604. Similarly, the clamping circuit 608 creates acurrent path with the diode 612, the auxiliary winding 304 of thesubconverter 604, and the power switch 616 of the subconverter 602.Thus, in the example of FIG. 6, the auxiliary winding 302, 304 and thepower switches 620, 616 can be considered components of the clampingcircuits 606, 608, respectively. As such, the switching device of theclamping circuits of FIG. 6 can be the diodes 610, 612 and/or the powerswitches 616, 620.

Additionally, although the forward power converters of FIGS. 1-6 includetwo subconverters, it should be understood that any one of the forwardpower converters disclosed herein may include two or more subconverters.For example, FIG. 7 illustrates multiphase interleaved forward powerconverter 700 substantially similar to the forward power converter 600of FIG. 6. The forward power converter 700, however, includes threesubconverters and three clamping circuits

As shown in FIG. 7, the forward power converter 700 includes asubconverter 702, the subconverters 602, 604 of FIG. 6, and threeclamping circuits 704, 706, 708 having diodes 718, 720, 722,respectively. The diodes 718, 720, 722 function similar to the diodes610, 612 of FIG. 6. Additionally, and similar to the subconverters 602,604, the subconverter 702 includes an input, an output, a transformer T3coupled between the input and the output, and primary side powerswitches 714, 716 (collectively a switching circuit) coupled to thetransformer T3.

The clamping circuits 704, 706, 708 create current paths to allow theauxiliary winding 302, 304, 724 to conduct during its respectivesubconverter's idle period as explained above. In particular, theclamping circuit 704 creates a current path with the diode 722, theauxiliary winding 302 of the subconverter 602, and the power switch 714of the subconverter 702. Similarly, the clamping circuits 706, 708create similar current paths using the diodes 718, 720, the power switch616 of the subconverter 602, the power switch 620 of the subconverter604, the auxiliary winding 304 of the subconverter 604, and an auxiliarywinding 724 of the transformer T3. Thus, and similar to the clampingcircuits 606, 608 of FIG. 6, each clamping circuit clamps a voltageacross an auxiliary winding by using a component of a differentsubconverter.

In some examples, the subconverters 602, 604, 702 may be phase shiftedsuch that an idle period of one subconverter at least partiallycoincides with a conduction period of only one subconverter. In suchcases, the clamping circuits 704, 706, 708 can be controlled asexplained above relative to a two subconverter system.

If, however, an idle period of one subconverter coincides with aconduction period of more than one subconverter, one or more clampingcircuits may be employed per subconverter in an “OR” logic manner tocover more than one conduction period. For example, one clamping circuitcan be coupled between the subconverter 602 and the subconverter 702 andanother clamping circuit can be coupled between the subconverter 602 andthe subconverter 604. The clamping circuits can be coupled together withan “OR” logic function (e.g., an OR gate, etc.) to ensure clampingcircuits cover more than one conduction period. In such examples, eachcurrent path created by the clamping circuit can include its owntransformer winding, rectifier, switching device, etc. In otherexamples, each current path can share one transformer winding and haveits own rectifier, switching device, etc. Alternatively, one clampingcircuit can be coupled between the subconverter 602 and thesubconverters 604, 702 via an “OR” logic function.

In some example embodiments, a switching device of the clamping circuitmay be controlled to create a current path. For example, FIG. 8illustrates a multiphase interleaved forward power converter 800including the subconverters 202, 204 of FIG. 2 having the transformersT1, T2, and clamping circuits 802, 804 coupled across a secondarywinding of the transformers T1, T2. The clamping circuits 802, 804 eachinclude a switching device 806, 808 and a diode 810, 812 coupled to theswitching device 806, 808. In the particular example of FIG. 8, theswitching devices 806, 808 are MOSFETs.

The clamping circuits 802, 804 may create current paths by using theswitching devices 806, 808, the diodes 810, 812, and the secondarywindings of the transformers T1, T2. These current paths can be brokenby controlling the switching devices 806, 808. For example, and as shownin FIG. 8, the forward power converter 800 includes subconverter drivecircuits 818, 820 and clamp drive circuits 814, 816 for generatingcontrol signals 822, 824 to control the switching devices 806, 808. Inthe particular example of FIG. 8, the control signals for the switchingdevices 806, 808 are based on a signal 826, 828 from the subconverterdrive circuits 818, 820.

The control signals generated for the switching devices 806, 808 may bebased on a parameter of the opposing subconverter. For example, and asshown in FIG. 8, the control signals generated by the clamp drivecircuit 814 for controlling the switching device 806 (coupled to thetransformer of the subconverter 202) is based on a signal 826 from thesubconverter drive circuit 820, which controls power switches of thesubconverter 204. Similarly, the control signals generated by the clampdrive circuit 816 for controlling the switching device 808 (coupled tothe transformer of the subconverter 204) is based on a signal 828 fromthe subconverter drive circuit 818, which controls power switches of thesubconverter 202.

Thus, when the subconverter 202 is in its conductive period and thesubconverter 204 is in its idle period, the subconverter drive circuit818 may provide the signal 828 indicating the subconverter 202 is in itsconductive period to the clamp drive circuit 816. The clamp drivecircuit 816 may then close the switching device 808 to create a currentpath for the clamping circuit 804 as explained above.

Although not shown in FIG. 8, additional isolation components may beused to provide desired isolation in the forward power converter 800.For example, gate drive transformers, optocouplers and/or other suitableisolation components may be used to pass signals between the primaryside and the secondary side of the transformers to control switchingdevices (e.g., one or both switching devices 806, 808, one or moreswitching devices of the subconverters 202, 204, etc.).

FIG. 9 illustrates a multiphase interleaved forward power converter 900similar to the forward power converter 800 of FIG. 8, but including athird subconverter. For example, the forward power converter 900includes the subconverters 202, 204 having the transformers T1, T2 andthe clamping circuits 802, 804 of FIG. 8, as well as a subconverter 902having a transformer T3 and a clamping circuit 904. Similar to theclamping circuits 802, 804, the clamping circuit 904 includes aswitching device 906 and a diode 908 coupled to the switching device906.

The switching devices of the clamping circuits 802, 804 are controlledby clamp drive circuits 814, 816 of FIG. 8, and the switching device 906of the clamping circuit 904 is controlled by a clamp drive circuit 910to create current paths as explained above. The clamp drive circuits814, 816, 910 are coupled to subconverter drive circuits 912, 914, 916,respectively. Although not shown in FIG. 9, the subconverter drivecircuits 912, 914, 916 control power switches in the subconverters 902,202, 204, respectively. Thus, similar to FIG. 8, the clamp drive circuitof FIG. 9 corresponding to an idle subconverter may close its switchingdevice to create a current path based on a control signal indicatinganother subconverter is in its conductive period.

In some embodiments, a switching device of a clamping circuit in aforward power converter having three or more subconverters may becontrolled based the other subconverters not coupled to that switchingdevice. For example, FIG. 10 illustrates a multiphase interleavedforward power converter 1000 similar to the forward power converter 900of FIG. 9. Each clamp drive circuit 814, 816, 910, however, generatescontrol signal(s) based on two subconverter drive circuit signals. Thus,control signal(s) to control the switching device of one clampingcircuit (corresponding to one subconverter) is based on signals forcontrolling power switches of the other two subconverters.

For instance, and as in FIG. 9, the subconverter drive circuits 912,914, 916 of FIG. 10 control the power switches of the subconverters 902,202, 204, respectively. The clamp drive circuit 814 generates controlsignal(s) to control its corresponding switching device coupled to thesubconverter 202 based on the subconverter drive circuits 912, 916.Similarly, the clamp drive circuit 816 generates control signal(s) tocontrol its corresponding switching device coupled to the subconverter204 based on the subconverter drive circuits 914, 912, and the clampdrive circuit 910 generates control signal(s) to control itscorresponding switching device coupled to the subconverter 902 based onthe subconverter drive circuits 914, 916.

Additionally and/or alternatively, control signal(s) generated for aswitching device of one clamping circuit may be based on a voltage of asubconverter not associated with that switching device. For example,FIG. 11 illustrates another multiphase interleaved forward powerconverter 1100 similar to the forward power converter 900 of FIG. 9. Theforward power converter 1100 includes the clamping circuits 802, 804,904 coupled across the secondary winding of the transformers T1, T2, T3of the subconverters 202, 204, 902, respectively. Each clamping circuit802, 804, 904 has a switching device and a diode coupled to theswitching device as explained above.

The forward power converter 1100 further includes clamp drive circuits1102, 1104, 1106 for controlling the switching device of the clampingcircuits 802, 804, 904, respectively. Thus, the clamp drive circuit1102, for example, may close the switching device of the clampingcircuit 802 to create a current path for that clamping circuit asexplained above.

As shown in FIG. 11, each clamp drive circuit 1102, 1104, 1106 receivesa voltage from a subconverter not associated with that clamp drivecircuit. The voltages may be, for example, sensed by any suitablevoltage sensing device.

For example, the clamp drive circuit 1102 receives a voltage(represented by a signal 1108) from the secondary side of thetransformer T3 of the subconverter 902, the clamp drive circuit 1104receives a voltage (represented by a signal 1110) from the secondaryside of the transformer T1 of the subconverter 202, and the clamp drivecircuit 1106 receives a voltage (represented by a signal 1112) from thesecondary side of the transformer T2 of the subconverter 204. Becausethe voltage is obtained from the secondary side of the transformers, thevoltage signals provided to the clamp drive circuits 1102, 1104, 1106 donot have to pass through isolation components.

FIG. 12 illustrates a multiphase interleaved forward power converter1200 similar to the forward power converter 1100 of FIG. 11, but whereeach clamp drive circuit 1102, 1104, 1106 receives a voltage input fromtwo subconverters not associated with that clamp drive circuit. Forexample, and as shown in FIG. 12, the clamp drive circuit 1106 receivesa voltage (represented by a signal 1202) from the secondary side of thetransformer T1 of the subconverter 202 and a voltage (represented by asignal 1204) from the secondary side of the transformer T2 of thesubconverter 204. The clamp drive circuits 1102, 1104 receive similarvoltage inputs from its from non-associated subconverters.

Although the forward power converters of FIGS. 8-12 illustrate clampingcircuits coupled to a secondary transformer winding, it should beunderstood that one or more of the clamping circuits of FIGS. 8-12 maybe coupled to another suitable transformer winding including, forexample, an auxiliary winding. For example, FIGS. 13 and 14 illustratemultiphase interleaved forward power converters 1300, 1400 similar tothe forward power converter 1000 of FIG. 10 and the forward powerconverter 1100 of FIG. 11, but with its clamping circuits coupled acrossa secondary side auxiliary winding instead of a secondary transformerwinding.

FIG. 15 illustrates another multiphase interleaved forward powerconverter 1500 similar to the forward power converter 1300 of FIG. 13,but having a different clamping circuit configuration. For example, theforward power converter 1500 includes clamping circuits 1502, 1504, 1506each including two switching devices coupled together. The switchingdevices are coupled in series with a secondary side auxiliary winding ofits associated transformer. For example, the clamping circuit 1502includes switching devices 1508, 1510 coupled in the series with thesecondary side auxiliary winding of the transformer T1 to create acurrent path as explained above. In the particular example of FIG. 15,the switching devices 1508, 1510 are MOSFETs, the drain terminals of theMOSFETs are coupled to opposing ends of the secondary side auxiliarywinding of the transformer T1, and the source terminals of the MOSFETsare coupled together.

The forward power converter 1500 includes clamp drive circuits 1512,1514, 1516 for controlling the switching devices of the clampingcircuits 1502, 1504, 1506, respectively, as explained above. Thus, theclamp drive circuit 1512, for example, may control one or both of theswitching devices 1508, 1510 to create a current path for the clampingcircuit 1502 as explained above.

Additionally, and as shown in FIG. 15, each clamp drive circuit 1512,1514, 1516 generates control signal(s) to control the switching devicesof each clamping circuit 1502, 1504, 1506 based on signals from twosubconverter drive circuits as explained above relative to FIGS. 10 and13. Alternatively, it should be understood that one or more of the clampdrive circuits 1512, 1514, 1516 may generate control signal(s) tocontrol the switching devices of each clamping circuit 1502, 1504, 1506based on one subconverter drive circuit signal as explained aboverelative to FIG. 9.

FIG. 16 illustrates a multiphase interleaved forward power converter1600 similar to the forward power converter 1500 of FIG. 15, but wherethe switching devices of each clamping circuit 1502, 1504, 1506 arecontrolled based on a voltage from one subconverter not associated withthat clamp drive circuit as explained relative to FIGS. 11 and 14. Forexample, the forward power converter 1600 includes clamp drive circuits1602, 1604, 1606 for controlling the switching devices of the clampingcircuits 1502, 1504, 1506, respectively. As shown in FIG. 16, theswitching devices 1508, 1510 of the clamping circuit 1502 are controlledbased on a received voltage (e.g., a sensed voltage, etc.) from thesecondary side of the transformer T3 of the subconverter 902. Theswitching devices of the other clamping circuits 1504, 1506 arecontrolled similarly, as explained above.

Alternatively, it should be understood that one or more of the clampdrive circuits 1602, 1604, 1606 may generate control signal(s) tocontrol the switching devices of each clamping circuit 1502, 1504, 1506based on a voltage from two subconverters as explained relative to FIG.12.

The clamp drive circuits of FIGS. 8-16 can include drive logic to derivea control signal for controlling switching devices of the clampingcircuits. The drive logic can optimize control of the switching devicesin conjunction with converter timing requirements for each subconverter.

Although FIGS. 2-16 illustrate each subconverter as including atwo-switch forward converter topology, it should be understood that anyother suitable forward converter topology including, for example, asingle switch forward converter, etc. may be employed. For example, FIG.20 illustrates a multiphase interleaved forward power converter 2000similar to the forward power converter 200 of FIG. 2, but including twosubconverters each having a single switch forward converter topology.

Additionally, although FIGS. 1-16 and 20 illustrate each subconverterincluding one switching circuit, it should be understood that one ormore of the subconverters may include multiple switching circuits. Forexample, FIG. 21 illustrates a multiphase interleaved forward powerconverter 2100 substantially similar to the multiphase interleavedforward power converter 700 of FIG. 7, but including two switchingcircuits per subconverter.

In particular, and as shown in FIG. 21, the interleaved forward powerconverter 2100 includes three subconverters 2102, 2104, 2106 eachincluding two switching circuits and a transformer T1, T2, T3 havingmultiple primary windings. Each switching circuit has a two-switchforward converter topology.

The subconverter 2102 includes a switching circuit 2108 coupled to aprimary winding 2110 of the transformer T1 and a switching circuit 2112coupled to a primary winding 2114 of the transformer T1. Likewise, thesubconverter 2104 includes a switching circuit 2116 coupled to a primarywinding 2118 of the transformer T2 and a switching circuit 2120 coupledto a primary winding 2122 of the transformer T2. The subconverter 2106includes a switching circuit 2124 coupled to a primary winding 2126 ofthe transformer T3 and a switching circuit 2128 coupled to a primarywinding 2130 of the transformer T3.

As shown in FIG. 21, the forward power converter 2100 also includesthree clamping circuits 2132, 2134, 2136 substantially similar to theclamping circuits 704, 706, 708 of FIG. 7. For example, the clampingcircuits 2132, 2134, 2136 each utilize an auxiliary winding of onetransformer T1, T2, T3, a diode, and a primary side power switch of oneof the switching circuits to function as explained herein.

The multiphase interleaved forward power converters disclosed herein mayinclude an inductor coupled to the outputs of each subconverter. Forexample, and as shown in FIGS. 2-21, each multiphase interleaved forwardpower converter includes an inductor Lo coupled between an outputcapacitor Co (e.g., representing a load) and the output of eachsubconverter.

As shown in FIGS. 2-21, the collective outputs of each subconverter arecoupled together in parallel to form an output stage of the forwardpower converters having a positive output terminal and a referenceoutput terminal. For example, the inductor Lo of FIGS. 2-16 and 18-21 iscoupled to the positive output terminal. Additionally and/oralternatively, any one of these inductors Lo may be coupled to thereference output terminal. For example, FIG. 17 illustrates a multiphaseinterleaved forward power converter 1700 similar to the forward powerconverter 200 of FIG. 2, but where the inductor Lo is coupled to areference output terminal. In particular, the subconverters 202, 204include a positive output terminal 1702 and a reference output terminal1704. As shown in FIG. 17, the inductor Lo coupled to the referenceoutput terminal 1704.

The inductors Lo disclosed herein may be one inductor, more than oneinductor if the inductors conduct during substantially the same timeperiod, more than one inductor if the inductors are magnetically and/orelectrically coupled together, etc. The inductor Lo may include theinductance of the inductor itself, parasitic inductance of othercomponents (e.g., wires, etc.), etc.

Additionally, the multiphase interleaved forward power converters mayinclude a rectification circuit coupled to the outputs of thesubconverters. For example, and as shown in FIGS. 2-18, 20 and 21, therectification circuit disclosed herein may include two or more forwardrectifiers (e.g., the rectifiers Rect1, Rect2 of FIGS. 2-6, 8, 17, 18and 20, the rectifiers Rect1, Rect2, Rect3 of FIGS. 7, 9-16 and 21,etc.) and a freewheeling rectifier (e.g., the rectifier Rect3 of FIGS.2-6, 8, 17, 18 and 20, the rectifier Rect4 of FIGS. 7, 9-16 and 21,etc.).

As shown in FIGS. 2-17, 20 and 21, each of the forward rectifiers arecoupled together in a common cathode configuration. That is, thecathodes of the forward rectifiers of FIGS. 2-17, 20 and 21 are coupledtogether. Alternatively, the anodes of the forward rectifiers disclosedherein may be coupled together to form a common anode configuration. Forexample, FIG. 18 illustrates a multiphase interleaved forward powerconverter 1800 similar to the forward power converter 200 of FIG. 2, butwhere the anodes of the forward rectifiers Rect1, Rect2 are coupledtogether.

Additionally and/or alternatively, the rectification circuits disclosedherein may include other suitable rectifiers including, for example, oneor more synchronous rectifiers. For example, FIG. 19 illustrates amultiphase interleaved forward power converter 1900 similar to theforward power converter 200 of FIG. 2, but including synchronousrectifiers sync rect1, sync rect2, sync rect3.

Further, the switching devices disclosed herein can be any suitablecomponent that breaks an electrical circuit. For example, the switchingdevices may be diodes (e.g., as shown in FIG. 5), switches such astransistors (e.g., MOSFETs, etc.), etc.

The multiphase interleaved forward power converters disclosed herein maybe powered by one or more power sources. For example, the powersource(s) may include a single front end rectifier, a multi-level frontend rectifier, a power factor correction (PFC) converter, etc. The powersource(s) may provide 230 VAC, 380 VAC, 480 VAC, 660 VAC, 690 VAC and/oranother suitable voltage. The power source(s) may be a single-phasesource or a polyphase source such as a three-phase source, etc.

For example, FIGS. 22A-22E illustrate the subconverters 2102, 2104, 2106of the forward power converter 2100 of FIG. 21 coupled to one or morepower sources. In particular, FIG. 22A illustrates the switchingcircuits 2108, 2112, 2116, 2120, 2124, 2128 of FIG. 21 each poweredindividually by its own power source 2202, 2204, 2206, 2208, 2210, 2212,respectively. Thus, each switching circuit is powered by a differentpower source.

FIGS. 22B and 22C illustrate the switching circuits 2108, 2112 (e.g.,the subconverter 2102) powered by one power source 2214, the switchingcircuits 2116, 2120 (e.g., the subconverter 2104) powered by one powersource 2216, and the switching circuits 2124, 2128 (e.g., thesubconverter 2106) powered by one power source 2218. As shown in FIG.22B, the switching circuits of each subconverter are coupled in serieswith its particular power source. Alternatively, and as shown in FIG.22C, the switching circuits of each subconverter can be coupled inparallel with its particular power source.

FIGS. 22D and 22E illustrate the switching circuits 2108, 2112, 2116,2120, 2124, 2128 of FIG. 21 all powered by one power source 2220. Theswitching circuits of FIG. 22D are coupled in series with the powersource 2220 while the switching circuits of FIG. 22E are coupled inparallel with the power source 2220.

The transformers disclosed herein may include any suitable primarywinding configuration, secondary winding configuration, and/or coreconfiguration. For example, FIG. 23 illustrates a transformer 2300including two sets of primary windings 2302, 2304, four sets ofsecondary windings 2306, 2308, 2310, 2312, an auxiliary winding 2314positioned between the two sets of primary windings 2302, 2304, and two“E” shaped core sections 2316, 2318. The secondary windings 2306, 2308,2310, 2312 can be coupled in series, in parallel, and/or a combinationof both depending on the desired output. The transformer 2300 of FIG. 23may experience good magnetic coupling and reduced leakage inductance dueto the multiple primary and secondary winding configuration.

The primary windings of FIG. 23 may be bifilar primary windings (asshown) and/or another suitable primary winding configuration if desired.The secondary windings of FIG. 23 may be formed of a wire conductor (asshown), a copper plate (e.g., for high current applications), and/oranother suitable secondary winding configuration if desired.

The transformer 2300 may be employed as any one of the transformers T1,T2, T3 of FIG. 21. For example, one set of primary windings (e.g., thewindings 2302) may couple to one switching circuit (e.g., the circuit2108) of FIG. 21 and the other set of primary windings (e.g., thewindings 2304) may couple to another switching circuit (e.g., thecircuit 2112) of FIG. 21. The auxiliary winding 2314 may be part of oneof the clamping circuits (e.g., the clamping circuit 704) of FIG. 21.The secondary windings 2306, 2308, 2310, 2312 may collectively representthe secondary winding of the transformers T1, T2, T3 of FIG. 21.

In such examples, the switching circuits coupled to the sets of primarywindings 2302, 2304 experience good power sharing (e.g., balancing) dueto the common transformer 2300 shared between the switching circuits.Additionally, the transformer 2300 achieves a compact and high-powerdensity design that saves space in power supplies compared to othertransformer configurations not including such features.

Further, windings of each of the transformers (e.g., the transformersT1, T2 of FIGS. 2-6, 8, 17, 18 and 20, the transformers T1, T2, T3 ofFIGS. 7, 9-16 and 21, etc.) may be placed on one transformer coreconfiguration. For example, FIG. 24 illustrates an example transformercore 2400 for a three phase interleaved forward converter, such as theforward converters of FIGS. 7, 9-16 and 21. As shown, the transformercore 2400 includes three “E” shaped core sections and an “I” shaped coresection. Windings of each transformer (e.g., the transformers T1, T2, T3of FIGS. 7, 9-16 and 21) can be placed on its own “E” shaped coresection. As such, the transformers T1, T2, T3 may share the transformercore 2400.

For example, windings of one transformer can be wound about the middleleg of one “E” shaped core section and windings of windings of anothertransformer can be wound about the middle leg of another “E” shaped coresection. In other examples, a transformer core may include two “E”shaped core sections and an “I” shaped core section for a two phaseinterleaved forward converter, such as the forward converters of FIGS.2-6, 8, 17, 18 and 20. Such transformer core designs increase powerdensity as compared to the transformer core of FIG. 23.

Additionally, although the multiphase interleaved forward powerconverters disclosed herein each include subconverters having the sametopology and clamping circuits having the same configuration, it shouldbe understood that different subconverters topologies and/or differentclamping circuit configurations may be employed for each multiphaseinterleaved forward power converter. For example, any one of themultiphase interleaved forward power converters can include asubconverter having one topology, another subconverter having adifferent topology, a clamping circuit having one configuration, and/oranother clamping circuit having a different configuration.

The multiphase interleaved forward power converters disclosed herein maybe employed in various applications. For example, the forward powerconverters may be used in variable output voltage power supplies,constant current power supplies, etc. Additionally, the forward powerconverters can be used as (or at least part of) power supplies forcomputing applications (e.g., servers, etc.), telecommunications,automation applications, imaging devices (e.g., magnetic resonanceimaging (MRI) devices, etc.), laser devices, medical/dental devices,semiconductor testing devices, etc.

By employing the clamping circuits disclosed herein, a resonance voltagemay be substantially prevented from propagating in subconverters ofmultiphase interleaved forward power converters during thesubconverters' idle period. For example, FIGS. 25-27 illustrate variouswaveforms of a drain to source voltage (Vds) of primary side switches ofthe forward power converters with and without resonance voltage. Theconduction period, the reset period, and the idle period for oneswitching cycle are identified in FIG. 25 for each subconverter withrespect to its voltage Vds waveform. For clarity, the conduction period,the reset period, and the idle period are identified in FIGS. 26 and 27for one of the subconverters with respect to its voltage Vds waveform.

FIG. 25A illustrates a voltage Vds (represented by line 2502) of aprimary side switch in one subconverter and a voltage Vds (representedby line 2504) of a primary side switch in another subconverter of aconventional multiphase interleaved forward power converter. Incontrast, FIG. 25B illustrates a voltage Vds (represented by line 2506)of a primary side switch in one subconverter (e.g., the subconverter 202of FIG. 2) and a voltage Vds (represented by line 2508) of a primaryside switch in another subconverter (e.g., the subconverter 204 of FIG.2) of a multiphase interleaved forward power converter having clampingcircuits as disclosed herein. As shown in FIG. 25B, the conductionperiod of one of the subconverters is at least partially complementaryto the idle period of the other subconverter.

As shown in FIG. 25A, a resonance voltage propagates through the primaryside switches during the idle period of each subconverter causing thevoltage Vds of the primary side switches to swing between about zerovolts and about 400 volts (e.g., the input voltage). In contrast, byusing the clamping circuits disclosed herein, a resonance voltage issubstantially prevented from propagating through the primary sideswitches. Thus, as shown in FIG. 25B, the voltage Vds of the primaryside switches remains steady at about 200 volts (e.g., about half theinput voltage due to the two-switch forward converter topology withclamping circuits) during the idle period of each subconverter.

FIGS. 26A and 26B illustrate similar waveforms as FIGS. 25A and 25B, butfor a multiphase interleaved forward power converter including threesubconverters. In particular, FIG. 26A illustrates voltages Vds(represented by lines 2602, 2604, 2606) of a primary side switch inthree subconverters of a conventional multiphase interleaved forwardpower converter. As shown in FIG. 26A, the voltage Vds swings betweenabout zero volts and about 400 volts multiple times due to a higher idletime resonant frequency caused by a lower transformer leakage inductanceand/or a lower switch capacitance as compared to, for example, thesubconverters represented in FIG. 25.

In contrast, FIG. 26B illustrates voltages Vds (represented by lines2608, 2610, 2612) of a primary side switch in three subconverters of amultiphase interleaved forward power converter having clamping circuitsas disclosed herein. Like in the voltage waveforms of the FIG. 25B, thevoltage Vds of the voltage waveforms of FIG. 26B remain steady at about200 volts during the idle period of each subconverter.

FIGS. 27A and 27B illustrate similar waveforms as FIGS. 26A and 26B, butfor a multiphase interleaved forward power converter having threesubconverters experiencing a lower idle time resonant frequency causedby a higher transformer leakage inductance and/or a higher switchcapacitance. In particular, FIG. 27A illustrates voltages Vds(represented by lines 2702, 2704, 2706) of a primary side switch inthree subconverters of a conventional multiphase interleaved forwardpower converter and FIG. 27B illustrates voltages Vds (represented bylines 2708, 2710, 2712) of a primary side switch in three subconvertersof a multiphase interleaved forward power converter including clampingcircuits as disclosed herein. As shown in FIG. 27B, the voltages Vdsremain steady at about 200 volts during the idle period of eachsubconverter.

Additionally, by employing the clamping circuits disclosed herein,transformer AC excitation caused by idle time resonance may be reducedcompared to conventional multiphase interleaved forward powerconverters. As a result, core losses due to idle time resonance may besubstantially eliminated, switching losses of primary side switches andsecondary side switches due to idle time resonance may be substantiallyeliminated, etc. As such, efficiency in forward power convertersincluding the clamping circuits increases relative to other conventionalforward power converters. This increased efficiency allows the forwardpower converters to meet industry compliance standards for variousdifferent rated loads. Further, the forward power converters includingthe clamping circuits include other benefits such as, for example,cancellation of ripple voltage and ripple current (e.g., on both theinput and output), reduction of required filtering, soft switching(e.g., zero voltage switching and/or zero current switching), etc.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A multiphase interleaved forward power convertercomprising: an inductor; a first subconverter comprising a firsttransformer coupled to an output of the first subconverter, the firsttransformer having at least one winding; a first clamping circuitcomprising a switching device coupled to the at least one winding of thefirst subconverter; a second subconverter comprising a secondtransformer coupled to an output of the second subconverter, the secondtransformer having at least one winding; first and second drivesconfigured to respectively operate the first and second subconverterswith cycling periods comprising: a conduction period during which poweris provided to the output of the respective first or second subconvertervia the respective first or second transformer; a reset period duringwhich energy stored in the respective first or second transformer isreleased to reset the respective first or second transformer; and anidle period between the reset period and the conduction period; whereinthe first drive is further configured to: phase shift the cyclingperiods in the first subconverter such that the conduction period of thefirst subconverter is at least partially complementary to the idleperiod of the second subconverter; and wherein the second drive isfurther configured to: phase shift the cycling periods in the secondsubconverter such that the conduction period of the second subconverteris at least partially complementary to the idle period of the firstsubconverter; and clamp a voltage across a winding of the transformer ofthe first subconverter to substantially prevent a first resonancevoltage from propagating in the first subconverter during the idleperiod of the first subconverter; wherein the output of the firstsubconverter is coupled in parallel with the output of the secondsubconverter; and wherein the outputs of the first and secondsubconverters are coupled to the inductor.
 2. The multiphase interleavedforward power converter of claim 1, wherein the first subconvertercomprises a pair of switching circuits, each switching circuit havingone or more power switches; wherein the at least one winding of thefirst transformer comprises a pair of primary windings; and wherein eachswitching circuit of the pair of switching circuits is coupled to arespective primary winding of the pair of primary windings.
 3. Themultiphase interleaved forward power converter of claim 1, wherein thefirst clamping circuit comprises a diode coupled to the switchingdevice.
 4. The multiphase interleaved forward power converter of claim1, wherein the second drive, in being configured to clamp the voltage,is configured to clamp the voltage across the winding of the transformerof the first subconverter based on at least one parameter of the secondsubconverter.
 5. The multiphase interleaved forward power converter ofclaim 4, wherein the second subconverter comprises a switching circuithaving one or more power switches coupled to the second transformer; andwherein the at least one parameter of the second subconverter comprisesa signal for controlling at least one of the power switches of thesecond subconverter.
 6. The multiphase interleaved forward powerconverter of claim 5, wherein the first drive is further configured toclamp a voltage across a winding of the transformer of the secondsubconverter based on at least one parameter of the first subconverterto substantially prevent a second resonance voltage from propagating inthe second subconverter during the idle period of the secondsubconverter; and wherein the first subconverter comprises a switchingcircuit having one or more power switches coupled to the firsttransformer.
 7. The multiphase interleaved forward power converter ofclaim 6, wherein the at least one parameter of the first subconvertercomprises a signal for controlling at least one of the power switches ofthe first subconverter.
 8. The multiphase interleaved forward powerconverter of claim 6, wherein the at least one parameter of the firstsubconverter comprises a voltage on a secondary side of the firstsubconverter.
 9. The multiphase interleaved forward power converter ofclaim 1 further comprising a rectification circuit coupled to the outputof the first subconverter and to the output of the second subconverter.10. The multiphase interleaved forward power converter of claim 9,wherein the rectification circuit includes one or more synchronousrectifiers.
 11. The multiphase interleaved forward power converter ofclaim 10, wherein the rectification circuit comprises a plurality offorward rectifiers and a freewheeling rectifier coupled to the pluralityof forward rectifiers; wherein each forward rectifier of the pluralityof forward rectifiers includes a cathode and an anode; and wherein thecathodes of each forward rectifier of the plurality of forwardrectifiers are coupled together.
 12. The multiphase interleaved forwardpower converter of claim 11, wherein the rectification circuit comprisesa plurality of forward rectifiers and a freewheeling rectifier coupledto the plurality of forward rectifiers; wherein each forward rectifierof the plurality of forward rectifiers includes a cathode and an anode;and wherein the anodes of each forward rectifier of the plurality offorward rectifiers are coupled together.
 13. A method for substantiallypreventing a resonance voltage from propagating in a multiphaseinterleaved forward power converter including an inductor coupled to anoutput of a first subconverter including a first transformer and anoutput of a second subconverter including a second transformer, theoutputs of the first and second subconverters coupled in parallel, themethod comprising: operating the first and second subconverters withrespective cycling periods, each cycling period comprising: a conductionperiod during which power is provided to the respective subconverteroutput via the respective transformer; a reset period during whichenergy stored in respective transformer is released to reset therespective transformer; and an idle period between the reset period andthe conduction period; phase shifting the cycling periods in the firstand second subconverters such that the conduction period of the firstsubconverter is at least partially complementary to the idle period ofthe second subconverter and such that the conduction period of thesecond subconverter is at least partially complementary to the idleperiod of the first subconverter; and clamping a voltage across awinding of the transformer of the first subconverter to substantiallyprevent a first resonance voltage from propagating in the firstsubconverter during the idle period of the first subconverter.
 14. Themethod of claim 13 further comprising clamping a voltage across awinding of the transformer of the second subconverter to substantiallyprevent a second resonance voltage from propagating in the secondsubconverter during the idle period of the second subconverter.
 15. Themethod of claim 13, wherein clamping the voltage comprises clamping thevoltage across the winding of the transformer of the first subconverterbased on at least one parameter of the second subconverter.
 16. Themethod of claim 15, wherein the second transformer has a primary sideand a secondary side; and wherein the at least one parameter of thesecond subconverter is a voltage on the secondary side of thetransformer.
 17. The method of claim 13, wherein clamping the voltagecomprises controlling a switching device of a clamping circuit to clampthe voltage across the winding of the transformer of the firstsubconverter.
 18. The method of claim 17, wherein the secondsubconverter comprises one or more power switches; and wherein theswitching device of the clamping circuit is a power switch of the one ormore power switches of the second subconverter.
 19. The method of claim17, wherein controlling the switching device comprises controlling theswitching device based on at least one parameter of the secondsubconverter.
 20. The method of claim 19, wherein the secondsubconverter comprises one or more power switches; and wherein the atleast one parameter of the second subconverter comprises a signal forcontrolling at least one of the power switches of the secondsubconverter.